Wind turbines convert kinetic energy from the wind into electrical power. A wind turbine is one of the cheapest ways to generate electric power as it uses a non-perishable natural resource that is free (unlike coal or oil) and exists most of the time in certain areas.
Wind turbines can rotate about either a horizontal (HAWT) or a vertical axis (VAWT), the former being both the older and the more common type. Every type of wind turbine has its own advantages and disadvantages. The main problems with most of the VAWTs are:                1. The blades of the classic turbines are found in an effective position relative to the wind direction for a short time only.        2. Their low rotation speed relative to HAWTs (in case of Savonius type turbines). The relatively low efficiency of this type VAWTs is caused by the difference between the drag forces of two blades which are located on opposite sides of the turbine. When one of the blades is on a first side of the turbine and “catches” the wind with its front side the turbine begins to rotate under the influence of the drag force on that blade. At the same time a second blade, which is on the opposite side of the turbine is also exposed to the same wind and drag force but from its back side resulting in a force that resists the rotation of the turbine.        3. In the case of Darrieus type of VAWT, external torque is required to cause initial rotation of the turbine.        
VAWTs have been described in many different structures. One such structure is disclosed in U.S. Pat. No. 6,926,491. In this patent the sails pivot about one vertical edge of the sail that is attached to a vertical pole distanced from the central shaft on an arm that is perpendicular to it. When the wind blows, the sails rotate about a vertical shaft. As the sails rotate sails moving towards the wind are automatically feathered. As they move away from the wind they are prevented by sail restraints from being feathered. A sail restraint catches the sail as it swings in the wind adding energy to the rotational force.
Amongst other factors, the magnitude of the drag force on an object is proportional to the area of the silhouette of the object on a plane perpendicular to the direction of the wind, to the square of the relative speed of the wind and the object, and to the drag coefficient. In order to increase the efficiency of the turbine it is necessary:                1. To decrease as much as possible the drag on the blade that opposes the rotation.        2. To cause the blade to “catch” the wind and be effective relative to the wind direction for a longer time.        3. To combine the effects of both lift and drag for the overall advantage of the operation of the turbine i.e. to allow for the blades be some time under lift force and some time under drag force.        
It is an object of the present invention to provide a system and method to increase the efficiency and the rotation speed of a Vertical Axis Wind Turbine (VAWT).
It is another object of the present invention to increase the drag force on the blade which rotates a VAWT and at the same time to orient the neighboring blade to decrease its drag force and to rotate the turbine by means of lift force.
Further purposes and advantages of this invention will appear as the description proceeds.